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Sunday, 31 July 2011

A Tour through the Aquarium: The livebearers

Ameca splendens male

The next tank to the Potosi pupfish contains several species of its fairly close relatives, the Goodeids. Unlike the egg-laying pupfish, Goodeids are livebearers. In any aquarium shop you will find for sale many species and colour varieties of livebearers, such as guppies, platies, and swordtails, which have been the target for selective breeding by aquarists for many years. These belong to another related group, the Poeciliids.

As a group the Cyprinodontiformes (the killifish group) is characterised by producing small numbers of large eggs that have long incubation times, and often some degree of internal fertilization. Retaining eggs within the body of the female until the point of hatching, then producing live young, is the commonest way in which live birth is evolved throughout the animal kingdom, and in the killifish it has evolved at least three times, in the Poeciliids, the Goodeids, and the strange four-eyed fish Anableps which lives in South America and along the coast.

Species which evolve an ecology based around production of comparatively small numbers of young tend to have limited dispersal ability, and as a result the killifish, both the egg-laying and live-bearing forms, tend to develop many endemic species. In the highlands of Mexico, where mountains have resulted in numerous small watercourses, this has resulted in large numbers of species with limited ranges. Unfortunately, agricultural development, deforestation, and introduced species such as trout can have a devastating effect on these small water bodies and their unique inhabitants, so many species of Goodeid are classed as threatened or worse.

Many species however breed very well in aquaria, and in most cases any home hobbyist could play a key role in preserving them. Some can be kept with other species in a typical mixed species home aquarium, but for breeding they deserve a tank of their own. For most species a temperature range around 22 degrees Celsius is best, and for most the diet is a standard aquarium flake food supplemented with vegetable matter.

Not all the species we have are on show, but among those in the display tank (which are producing young regularly), are these:

Ameca Splendens Butterfly Goodeid

A.splendens female

This is one of the larger species – females can grow to 12 cm. Males are usually much smaller, and can be distinguished by the vertical black and yellow stripe in the tail. This is a very common feature in male Goodeids. It originates from the Ameca river drainage, and today is known in the wild only from a single pond closed to Ameca town, which apparently is used by the locals for washing cars, so the risk of a pollution incident wiping out the last wild population must be extremely high. They can be a little aggressive in an ordinary home aquarium, so a species tank is best for them. They are however easy to keep and breed providing their needs for space is met – unlike some other livebearers they seldom feed on the fry, which are quite large at birth.

Ataenobius toweri: Bluetail goodea

A.toweri

Originating from the Rio Verde, this likes a similar set up to Ameca splendens, except slightly warmer. It is classed as Endangered on the IUCN red list. The generic name relates to the apparent lack of trophotaenia, outgrowth of the lower intestine in the unborn young that absorb nutrients from the parent in the same way as a mammalian placenta, which are universal in Goodeids. It now appears that these are merely smaller than usual and regress completely before birth. It is likely that it will be transferred to the related genus Goodea at some point.

Characodon lateralis Rainbow characodon

C.lateralis

Endemic to the state of Durango, this species may be extinct in the wild. A subtropical species, it lives in streams and is very sensitive to water pollution, which is a probable cause of its disappearance. It needs frequent water changes and good filtration in an aquarium, and like other Goodeids a large vegetable component in the diet. It seems to benefit from cooling down in the winter months, and is probably a seasonal breeder. The young can be quite large and are not especially bothered by the parents.

Zoogoneticus tequila Crescent Zoe

Z.tequila (male)

Critically Endangered, and possibly extinct in the wild, the Crescent Zoe was only described in 1998. It formerly inhabited the Rio teuchitlan in the Ameca river drainage system, and was believed extinct in the wild until a tiny population (only about 500 in total including fry) was found in one small pool. They are difficult to breed, being shy and slow growing. It appears to prefer less stony substrates than the stream dwelling Goodeids, but this may be a result of the destruction of preferred habitat, as several of the source streams of the river have been converted into spas.. Several aquarists are maintaining this species in aquaria in both the US and in Europe.

That covers the livebearers we currently keep at Bristol. Given the vast size of the aquarium market, there is considerable scope for home aquarists to provide vital space to maintain the smaller species of threatened fish, but working out administration of any breeding programme is proving problematic. Anyone interested in helping should contact one of the specialist aquarist societies such as the British Livebearer Association (http://www.britishlivebearerassociation.co.uk ) or the American Livebearer Association (http://livebearers.org ). For the egg-laying killifish, contact the British Killifish Association (http://www.bka.org.uk ) or the American Killifish Association (http://www.aka.org/aka/ )